1. Field of the Invention
The present invention relates to an intermediate transfer member to be mounted on an electrophotographic apparatus and an electrophotographic apparatus.
2. Description of the Related Art
The following intermediate transfer system has been employed in some of color electrophotographic apparatus. Developed images of four colors, i.e., yellow, magenta, cyan, and black colors are transferred from a photosensitive member onto an intermediate transfer member in a superimposed manner, and then the images are collectively transferred onto a printing medium such as paper.
In such intermediate transfer system, a secondary transfer process involving transferring a toner image on the intermediate transfer member onto the printing medium exists. In addition, in the secondary transfer process, the following has been performed for efficiently transferring the toner image onto the printing medium. A transfer roller and an opposing roller are disposed opposite to each other across the intermediate transfer member, and a secondary transfer voltage is applied between the transfer roller and the opposing roller.
Meanwhile, the following has been proposed for further improving the efficiency with which the toner image is transferred onto the printing medium in the secondary transfer process. The surface of the intermediate transfer member on a toner image-bearing side is provided with a functional layer for improving the releasability of the toner image.
Japanese Patent Application Laid-Open No. 2012-68344 proposes an endless belt for an image-forming apparatus, the belt having a surface layer whose outermost surface is constituted of a composite resin composition containing: 25 to 80 mass % of a fluorinated polyimide resin having an ether group on its main chain; 10 to 65 mass % of a fluorine resin; and 10 to 50 mass % of conductive particles. In addition, Japanese Patent Application Laid-Open No. 2012-68344 discloses that according to such endless belt, good releasability of a toner image can be held over a long period of time.
By the way, the inventors of the present invention have found that in an image-forming apparatus using an intermediate transfer member having a surface subjected to a treatment for improving the releasability of a toner image with a fluorine-based resin, secondary transfer efficiency may gradually reduce as the number of printed sheets increases. In addition, the inventors of the present invention have conducted an investigation on a cause for the foregoing. Then, the inventors have found that the amount of fluorine atoms on the surface of the intermediate transfer member reduces as the number of printed sheets increases, and as a result, the toner releasability of the surface of the intermediate transfer member reduces to lower the secondary transfer efficiency. The reason why the amount of the fluorine atoms on the surface of the intermediate transfer member reduces as the number of printed sheets increases is assumed as described below. The application of the secondary transfer voltage between the transfer roller and the opposing roller causes discharge between the surface of the intermediate transfer member and the transfer roller, and the fluorine-based resin on the surface of the intermediate transfer member, albeit in a slight amount, is decomposed by the discharge.